text:
How unusual is the 737 MAX 8's crash history?
The Boeing 737 MAX 8 is getting a lot of bad press at the moment,  but people's instincts when it comes to probability are generally terrible, especially when it comes to risk assessment.
Compared to other models, how unusual is it for there to be two crashes in half of a year, of rather young planes? How much total flight time has the model had? How statically signification is it?

Historically, it's not unusual at all to have many accidents of an aircraft type in relatively short order, especially when the type is still new and hasn't had a lot of operating hours across the fleet to detect and work out teething problems.
BUT, and that's a big BUT, in recent history that's been happening less and less as testing and certification programs have gotten ever longer and stricter (in large part as a result of those earlier crash series).
As for the 737Max, according to Wikipedia some 350 have so far been delivered (out of over 5000 on the order book) over the space of only 2 years (yes, they're that new). Of those 2 have gone down. That's not a particularly high number historically, but as said in recent history people have come to expect nothing bad to ever happen because there have been so few accidents overall and most of those easily explained by external factors (MH17 being shot down, for example).
So this number is both highly unusual, in that it's not something that's been seen in recent memory, and rather normal, in that in the history of aviation it's not unusual at all.

"Highly unusual.. and rather normal" Nice summary!

So, 2/350 ~= 0.5% crashes is "not a particularly high number"? I realize that's not 0.5% of flights, but still. Are you sure?

@einpoklum it isn't, historically. Extreme case is Concorde, with 1/14 crashes or about 12%. Out of about 700 DC-6s 185 were lost or over 26%. Tu-154 had about 1000 built and 69 hull losses, or about 7%. I just count hull losses here. So no, the number is in no way particularly high. It's only more than a statistical blip because both losses happened in under 2 years since the type entered service.

@jwenting: Within 2 years...

@jwenting: Actually, an "extreme case" would be the de Havilland Comet 1/1A - 7 hull losses out of a total of 22 produced (32%), all within a year and a half (26 October 1952 - 8 April 1954).

The B737MAX is not e brand new type though, just the latest edition of a family that has been around for half a century.


text:
Question about congestion of the 1090MHz frequency
I'm no expert so there's likely to be a lot of mistakes in this post.
ADS-B - Automatic Dependent Surveillance - Broadcast, (out) transmits (in) receives position data from/to other aircraft and to ATC.
I've been trying to find out more about how congestion of the 1090MHz frequency will be addressed. It seems that ADS-B out is becoming fairly ubiquitous. Additionally, there will be more aircraft interrogating (on 1030MHz) and responding to interrogations on 1090MHz for transponder based systems (TCAS, SSR). From this post, it sounds like things are already congested in some areas.
Here are some of the things that I'm unable to google for so far:

On the wikipedia page for TCAS, there is mention of a bandwidth limitations of 1 megabit/second. What does this mean?:

a) Within an airspace only 1 megabit/second of data can be transmitted cumulatively.
b) Air traffic control can only receive 1 megabit/second.
c) Individual aircraft can only transmit 1 megabit/second.
d) The receiving equivalent of c.
e) Other

What is physically limiting bandwidth? Will there eventually just be too much interference between signals whilst using this frequency, or is it a hardware issue? I couldn't seem to google this issue, maybe I need some keywords.

Are the solutions to increasing capacity about being more clever with how the packets are sent (more efficient packet sizes, fewer packets, better/cleaner transmission), improving ground or air hardware, or is there a "add more lanes to the highway" solution? It seems 978MHz is equivalent to adding more lanes.

What is the consequence of congestion? Are packets corrupted as noise rises? What keywords should I google?

Also, thanks for all the useful info on this site, aced a Masters assignment recently because of the aircraft designers on here.

This honestly may be more of an Electrical or Wireless engineering question. Though I'm not sure there's another SE community that would be better at answering it.

@zymhan you're probably right, but I wasn't sure whether the limitations, particularly bandwidth, were specifically related to an aviation issue or if it was a more general issue.

Additionally, there will be more aircraft interrogating (on 1030MHz) and responding to interrogations on 1090MHz for transponder based systems (TCAS, SSR).

Actually, no. More Mode S (vs Mode A/C) aircraft means TCAS can use Selective interrogation instead of All-Call interrogation, which will reduce congestion from unnecessary replies.
Also, newer TCAS systems are ADSB-aware and will reduce (not stop, for safety reasons) even their selective interrogation rate for ADSB targets, further reducing congestion.
Also also, part of the goal of ADSB is to reduce the need for SSR overlap, which will greatly reduce congestion as well.

... bandwidth limitations of 1 megabit/second. What does this mean?

Remember that this is a spatially distributed system, so congestion observed varies for each receiver based on which subset of transmitters they can hear. How far you can hear depends mostly on how high your antenna is.
The bandwidth number is a theoretical maximum data rate based on the bits per message and number of messages per second, assuming no overlap and no gaps. It will never happen in practice; it’s only useful as a yardstick for the current data rate.

What is physically limiting bandwidth? Will there eventually just be too much interference between signals whilst using this frequency,

Yes, see above.

Are the solutions to increasing capacity about being more clever with how the packets are sent (more efficient packet sizes, fewer packets, better/cleaner transmission),

The protocol is already as clean and efficient as it can be while remaining compatible with older Mode S equipment.
Most of the congestion comes from frequently sending redundant data as a crude form of FEC. Turn that off and congestion would go away, but so would the ability to gracefully degrade.

improving ground or air hardware,

One vendor (Airspy) claims to be able to decode overlapping messages, which if true would drastically reduce data loss and raise the practical bandwidth above the theoretical maximum. But I don’t know how well it works in practice or whether anyone is pursuing this for certified hardware.

or is there a "add more lanes to the highway" solution? It seems 978MHz is equivalent to adding more lanes.

That is allegedly why the FAA pushed UAT978 for light GA aircraft in the US.

What is the consequence of congestion? Are packets corrupted as noise rises?

The only real problem is collisions, not noise. Unless you define unreadable-due-to-collision messages as noise, of course.
The consequence is simply that you miss any data whose message was unreadable. However, the protocol was specifically designed to be highly redundant to minimize the impact of low to moderate levels of loss. Exactly how much loss it can tolerate is not clear, but so far it doesn’t seem to be a problem in practice.

Thanks, this answers everything and has given me a lot to look into. Couple more quick questions. Are "overlapping messages" and "collisions" the same thing? And, is there much current engineering research (such as Airspy) into raising bandwidth, or is there little incentive and technology to deal with the problem in a novel way?
I have found 3-4 papers on the topic, I'll list them in my post once I get back to my computer.

@RoryMcDonald Yes, overlap and collision are the same thing. Unlike WiFi or cell networks, 1090 has no mechanism to prevent collisions; it relies purely on FEC. There is no way to improve the bandwidth and remain compatible with existing Mode S equipment.

Another quick question, I've seen the term "ADS-B transponder", is this a misnomer? I thought transponder implied interrogation-repsonse was occurring, whereas ADS-B is automatic.

Technically, ADSB Out is a squitter. However, these are frequently integrated into a Mode S transponder, and the result is referred to as an “ADSB transponder”.

Ah I see, thanks.

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text:
Do aircraft that operate at lower altitudes tend to have more cycles?
I've heard that aircraft cycles depend on the number of missions, regardless of the distance, because the pressurisation of the aircraft at altitude is what causes cumulative damage to the fuselage. If that's the case then does it tend to be true that aircraft that fly lower have more cycles? I'm particularly wondering about the difference between turboprop (FL240) and jet aircraft (FL410). Do turboprop fuselages tend to have more cycles?

Is it also possible that aircraft that have more cycles (i.e. operate shorter missions) tend to fly lower?

It's a lot more than just pressurization cycles (all sorts of things are being flexed), but yes. Turboprops are somewhere around 1 hour per cycle and regional jets about 1.2 or 1.3 hours per cycle (a typical regional jet will do around 3000 flying hours and about 2400 cycles in a year).  Mainline jets are closer to 2+ hours per cycle, with long haul jets around 3-4 hours per cycle.
So a turboprop with 50000 hours will tend to have 50000 cycles (averaged across the fleet), the RJ with 50000 hours will have around 40000 cycles, while a 777 with 50000 hours might only have 20000 cycles (keeping in mind wide variations from aircraft to aircraft).
So yes the short haul commuter and regional equipment does get flogged like mules compared to their luxuriating mainline big brothers.  Whether this becomes a "premature" problem depends on how robust the original design was.  The beefier the metal with a given load profile, the more times you can flex it before it starts to crack.  But when you make it beefier, you are adding "ballast" from the perspective of the short term mission. So it's a trade off between performance now, and viability when the airframe gets old (the extra beef reduces payload upfront, but adds greatly to the residual value of the airframe 20 years later - some operators will prefer one approach, some the other).
When the first high-time DeHavilland Dash 8 got to 80000 cycles, the original structural life expectancy, they only found a couple of minor cracks. This eventually led to an extension of the structural life limit to 120,000 cycles, giving a huge boost to the market value of old Dash 8s.  Airlines that own their Dash 8 cared greatly about this.  Airlines that leased their airplanes knowing they'll turn them in at a certain point long before, not so much.
CRJs on the other hand, are bit less robust and a CRJ200 needs quite a bit of patching of the structure after 40000 cycles to keep it viable to its 80000 cycle airframe life (a consequence of not doing a full fatigue test program at the very beginning - they only tested a fuselage barrel, with the full program being done about 8 years later). You can keep flying it past 40000 cycles without the reinforcements, but the frequency of the repetitive inspection requirements imposed make that uneconomical.
On the other hand, the cost of all the patches was brutal, and a lot of CRJ200s were simply retired at 40k, and their airframes stripped for spares, because the operators didn't want to spend the money to incorporate all the structural Service Bulletins (Embraers like the 145 are even lighter in their construction and considered even more "disposable" - a 145 once had its back broken, became an instant tail dragger, on a hard-ish landing in Brazil, a landing that wasn't hard enough to blow tires).
None of this really impacts safety if the maintenance program was developed properly, because inspection intervals and procedures prevent structural issues from progressing to a dangerous level, plus damage-tolerant structural design and very large (3:1) scatter factors applied to fatigue test results (if you bend a component repetitively in a fatigue rig, and it starts to crack at 60000 cycles, you have to impose an inspection or repair or life limit of some kind at 20000 cycles).
Notwithstanding "outlier" events like Aloha Airlines. Things always get through the cracks.

Does a non-pressurized aircraft have a fatigue life at all?

Sure; most of  the loads, wing bending, tail bending, landing gear structure, are cycle sensitive to some degree.  The wings flexing up with flight loads and flexing back down on landing is a cycle. Also turbulence loads are factored in based on a set of assumptions of the number of flex loads from turbulence per average cycle, that sort of thing and are worked into the mix for a fatigue test program.  The 3:1 scatter factor used is to cover the variability in assumptions and calculations.

Seems like the DC-3 is immortal, though.

It's in the upper range of the fatigue curve, being designed with slide rules and only a moderate grasp of the metallurgy of the time, so there was ample extra beef added to be safe.  I found an article from 2015 saying the highest time 3 had 92000 hrs. If you put a 3 in a fatigue rig, I'd bet it would qualify for a 100000-15000 hour life. Cessna once bought a 12,000 hr 172 used for pipeline patrol, the highest time most beat up one they could find, to see if the airframe was suffering, and found all it needed was new hinge bearings.

Aircraft fatigue life is generally defined in terms of cycles and flight hours. Cycles better reflect the damage created by shock loads, as occurs in taxiing (braking/turning on ground), takeoff (high power/vibration, load transfer from landing gear to wings) and landing (impact, braking). However, the aircraft is still under cyclic loads caused by engine vibration and turbulance in cruise and that also consumes fatigue life. For this reason, aircraft have cycle and flight hour limits for overhauls (where components are checked for microcracks) and total life limits where the component or the entire aircraft is scrapped.
Turboprops have relatively higher cycle life wrt a jet airliner, but this is not related to cruise altitude or any particular trait of turboprops. Instead, the aircraft is designed to reach its cycle and flight hour limits simultaneously, so that the aircraft can serve for as long as possible.
Turboprops have higher cycle limits because their flight legs are shorter relative to jets.

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text:
Why should Mach wave angle be less than wing sweep angle?
This is from my lecture notes:

I see that this is so you can have subsonic flow over the wing planform, but why is this desirable? And are there more reasons?
I can think of heat being an issue if you have a strong shock wave forming on the wing. But I recall that pressure will also increase after a shock, so perhaps there is a reason why you might want the shock to occur inside the wing area? Just guessing at this point.

Short answer: Leading edge thrust.
Slightly longer answer: Subsonic flow has the capacity to negotiate the leading edge, resulting in a suction peak which is missing in supersonic flow. Sweep allows to keep that flow pattern for as long as the flow speed component perpendicular to the leading edge is subsonic.
This suction peak, acting on the forward-facing surface of the leading edge, pulls the wing forward, hence the expression "leading edge thrust". This is missing once the perpendicular speed component exceeds Mach 1, exposing the forward-facing area of the wing to the increased pressure aft of the shock.
This characteristic can be maximized by conical camber, a cambering of the most forward part of the airfoil which increases with span, such that the outer forward wing has a conical surface. This has been introduced with the F-106 and is used on many supersonic designs.

F-106 at an angle to the sun which nicely shows the cambered leading edge (picture source)

@ymb1 1) It is integrated and partially explains the d'Alembert paradox. 2) The outer LE has the most distance to the shock so here the subsonic pattern is "purest" and allows to use LE thrust the most.

Thanks! Why is this effect harnessed more in supersonic aircraft when surely it could be applied to a transonic aircraft with an equivalent leading-edge-perpendicular Mach number? I feel like there is more to the rule of "flow perpendicular to the leading edge is what's important".

@RoryMcDonald Yes, there is. Please read this for an explanation what is so special about Mach 1. Sweep will lessen and smooth out the drag peak at the sound barrier. That is the most important reason for sweeping wings. And of course all sub- and transsonic airplanes use leading edge thrust. That is one reason why subsonic flight is so much more efficient; the other is of course the compressibility expansion effect at supersonic speed which is explained in the linked answer.

TLDR; Subsonic perpendicular flow over the wing's front edge lets you optimise the wing for the subsonic take-off and landing.
Don't be mistaken! The flow itself is still supersonic and you will still have to deal with shockwaves on your wing! You will not have (or at least it is very undesirable to have a strong shockwave in front of the aircraft) subsonic conditions over the wing. The perpendicular flow however is not and that what counts for the leading edge.
The leading edge of the wing should be as sharp as possible in a supersonic regime. Curves cause severe drag as multiple infinitesimal shockwaves form and combine into one large one. (In theory it would converge to adiabatic compression which is not at all true for the real case)
However, a plane has to take-off in subsonic flight and if you don't have a TWR>1 you'll need your sweet sweet lift, and for this case, a sharp edge is incredibly unfortunate as it will create a very turbulent airflow or even worse separation due to flow from the bottom to the top over the front edge. Therefore, if the perpendicular flow is subsonic you can use a rounded front edge, helping you with take-off and landing.
If you want a very fast plane, (e. g. Ma > 3) you will have troubles as super swept wings won't help you with TO and LDG. Some fighters therefore have adjustable wings but that's a nightmare for safety reasons. In civilian aviation that's not gonna happen any time soon. -> You'll have to consider all your regimes during a mission. A plane that's super efficient in Ma>5 with it's SCRAMJET engines that's not able to TO on it's own is pretty much useless. Same with the wings.

That's at least the first thing that comes to my mind reading the question. In case I missed something I'll extend the answer.

Thanks for the answer. I think perhaps my lecturer has simplified things. Since we're using Mach number flow tables we always look at examples of strong shock, and therefore flow is actually subsonic in most of the examples given.

That's quite the simplification. The only place a strong shock is desired is in RAMJETs but ongoing research tries to eliminate that, since it's very inefficient, but supersonic burn isn't easy either.
I remember we got a delta arrangement with 3D profile and had to calculate all the way through and then once again inside the RAMJET with reflections and all. It isn't complicated but just a lot of work...

As explained in another answer, keeping the wing inside the shock cone maintains the subsonic pattern of sideways flow which causes air to flow up around the leading edge. This allows you to use a rounded leading edge, which also works well at low speeds.
But allowing the shock to meet the leading edge is not all bad. This is the condition in which the waverider operates, the Mach 3 capable North American XB-70 Valkyrie being perhaps the most notable example. The trick is to use the shock pressure on the underside to create lift, but to avoid it on the upper surface.

Thanks, just asked Peter Kampf if leading edge thrust could be used at low speeds.
By "meet the leading edge" you mean to just touch the leading edge, correct? Not go past it? Can the same effect be created with a bow shock, or is there too much drag involved?

@RoryMcDonald attaching along the length of the leading edge maximises wave lift. The whole leading edge creates its own shockwave along itself; as I recall any outward-propagating shock merges with it and doesn't "get past" it (not entirely sure). A bow shock cannot attach to the inner leading edge unless the plane is a flying wing or lifting body with no fuselage forward of the lifting surface: most if not all modern experimental waveriders are of this type.


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What are autothrust and manual thrust on an A320 (or other aircraft)?
The accident report on the A319 G-EUOE incident in May 2013 mentions "manual thrust", and implies that using it is very unusual.
The autothrust system failed, requiring the use of manual thrust:

The autothrust system cannot operate  in N1 mode and so was
  unavailable for the remainder of the flight, which was  flown using
  manual thrust

But the pilot hadn't used manual thrust outside a sim session for seven years (and the co-pilot had never used it outside the sim):

The commander informed the AAIB that, excluding simulator training, he
  had  last flown the A320-series aircraft using manual thrust seven
  years before the accident

That implies that autothrust is always used in normal operations, and manual thrust is an emergency backup only. What exactly are autothrust and manual thrust and why is using manual thrust so unusual?

Manual thrust means that the engine thrust corresponds directly to the position of the thrust lever.
Autothrust means that a target speed is dialed into the system (using a knob that is usually located on the glare-shield) and the auto-thrust system automatically adjusts the engines to maintain that speed.
Now in an aircraft with classical controls the longitudinal stability means the aircraft tends to maintain speed with pitch and pilots basically need to use thrust to climb or descend and yoke to adjust speed, always making adjustments with the other control as well to avoid oscillations and compensate for the more complex parts of the power-pitch relationship.
Due to this, it is usually recommended to fly either fully manual or fully automatic (autopilot+autothrust).
But Airbus A320 and newer (A319 is just a variant of A320) changes that with the artificial neutral stability in normal control law. Even with autopilot off, the flight computer automatically adjusts trim so that the aircraft flies straight so that adding power makes the aircraft accelerate and reducing it makes it decelerate. However pushing the stick forward to descend will still make the aircraft accelerate and pulling it to climb will make it slow down.
Due to this, Aibrbus aircraft are easier to fly with autothrust always on (except for take-off roll; autothrust is disabled when the power levers are advanced above certain position, which is only done for take-off and in emergency where extra power is needed).

I have had zero issues regarding landing an Airbus with autothrust off. It handles pretty much like any other aircraft.

To add one piece of information to Jan's answer, quoting from the A320 Flight Crew Training Manual, a detailed description of what exactly is autothrust:

OBJECTIVE
The A/THR computer (within the FG) interfaces directly with the engine computer, referred to as the FADEC. The A/THR sends to
  the FADEC the thrust targets that are needed to:
• Obtain and maintain a target speed, when in SPEED mode
• Obtain a specific thrust setting (e.g. CLB, IDLE), when in THRUST
  mode.
INTERFACE
When the A/THR is active, the thrust lever position determines the maximum thrust that the A/THR can command in SPEED or
  THRUST mode. Therefore, with A/THR active, thrust levers act as a
  thrust limiter or a thrust-rating panel. The A/THR computer does not
  drive back the thrust levers. The PF sets them to a specific detent on
  the thrust lever range.
The A/THR system provides cues that indicate the energy of the
  aircraft:
• Speed, acceleration, or deceleration, obtained by the speed trend
  vector
• N1, and N1 command on the N1 gauge.
All these cues are in the flight crew’s direct line of vision. In
  other words, the Thrust Lever Angle (TLA) should not be used to
  monitor correct A/THR operation. Neither should the thrust lever
  position of a conventional autothrottle, be considered a cue because,
  in many hazardous situations, the thrust lever position can be
  misleading (e.g. engine failure, thrust lever jammed).

The A/THR can only be active, when the thrust levers are between IDLE
  and the CLB detent.
  When the thrust levers are beyond the CLB detent,
  thrust is controlled manually to the thrust lever Angle, and the A/THR
  is armed . This means that the A/THR is ready to be re-activated, when
  the flight crew sets the thrust levers back to the CLB detent (or
  below).A/THR appears in blue on the FMA.

In addition:

If thrust levers are set to IDLE, A/THR is set to off.

and:

AP, FD, A/THR SYSTEM INTEGRATION
There is a direct relationship between aircraft pitch control, and engine thrust control. This
  relationship is designed to manage the aircraft’s energy.
• If the AP/FD pitch mode controls a vertical trajectory (e.g. ALT,
  V/S, FPA, G/S): A/THR controls speed
• If the AP/FD pitch mode
  controls a speed (e.g. OP CLB, OP DES): A/THR controls thrust (THR
  CLB, THR IDLE)
• If no AP/FD pitch mode is engaged (i.e. AP is off and
  FD is off): A/THR controls speed
Therefore, any change in the AP/FD pitch mode is associated with a
  change in the A/THR mode.

On the other hand, manual thrust is a conventional and proportional interpretation of the position of the TLP: 0% throttle at IDLE, 100% at TOGA  and linearly interpolated inbetween.

As for why the A/THR is seldomly not used, from the same manual (emphasis mine):

Use of A/THR is recommended during the entire flight.
  It may be used in most failures cases, including:
• Engine failure, even during autoland
• Abnormal configurations

Autothrust is basically automatic thrust. On approach to landing the autothrust is in SPEED mode. That is, as the pilot varies the pitch of the aircraft, the thrust is either added or removed to keep the aircraft on the calculated approach speed. For example, if the pilot pitches the nose up on approach, the speed of the aircraft drops so the autothrust increases engine thrust to catch the speed and vice versa.

The inner workings of Airbus autothrust.
http://wtruib.ru/training_A320F/autothrust-presentation/
The pilots also have the option to turn off the autothrust and control the thrust of the engine by him or herself. This is called manual thrust. It is as simple as that. So, with manual thrust the pilot will control both the aircraft trajectory and the speed.
Is it unusual for an Airbus pilot to not use the autothrust? No, not all. I am an Airbus pilot and I use manual thrust occasionally to keep my manual flying skills up. Is it difficult? Again, no. With autothrust off it flies just like any other aircraft without an autothrust system. I have many hours as an airline pilot in an aircraft that had no autothrust. To be honest with you, at times I find it easier to land an Airbus with the autothrust off because it allows me to really feel the energy state of the aircraft. I do not know about other pilots but when I did my initial type rating on Airbus, the first three sessions were all done with mostly autothrust off. Interestingly, me and my training partner initially struggled with autothrust on landings, because it was weird for us not to have control of the thrust after many hours of flying the Dash 8.
There are some airlines that ban the usage of autothrust on landing. One of them is Lufthansa. My airline is more flexible regarding that. It is up to the pilot to decide to use it or not. Then there are airlines that says specifically not to turn the autothrust off. Still the pilots of those airlines will practice autothrust off landings during their 6 month recurrent trainings.
I am sorry but I cannot really comment on why the captain did not turned off the autothrust for almost 7 years. Airline policy or his preference? Not sure. But he was able to land the aircraft well. So, he had the ability to do it, when it was required.

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What does the FAA consider to be "good moral character"?
Per 14 CFR 61.153(c) candidates for an ATP license must "be of good moral character".
What does that actually mean and how does an examiner or the FAA verify it?

I believe that cheating on an exam or lying about flight experience is considered "bad moral character".

and wouldn't be surprised if they also check criminal records for things like drugs related charges.

"When the FAA uses a wordit means just what they choose it to mean — neither more nor less." - With apologies to Humpty Dumpty :)

An examiner uses the contents of FAA Order 8900.1 - Flight Standards Information Management System (FSIMS)as guidance for doing their job.
As you might imagine, there is some guidance available for them there:

VOLUME 5 (AIRMAN CERTIFICATION)
CHAPTER 2 (TITLE 14 CFR PART 61 CERTIFICATION OF PILOTS AND FLIGHT INSTRUCTORS)
Section 18 (Conduct an Airline Transport Pilot Certification, Including Additional Category/Class Rating)
Paragraph 5-704 (ELIGIBILITY –ATP CERTIFICATE – AIRPLANE, ROTORCRAFT, AND POWERED LIFT):
C. Good Moral Character Requirement:
  An applicant must be of good moral character. The inspector must ask an applicant if the
  applicant has been convicted of a felony. If the applicant’s answer is
  affirmative, the inspector should make further inquiry about the
  nature and disposition of the conviction. If an inspector has reason
  to believe an applicant does not qualify for an ATP certificate
  because of questionable moral character, the inspector must not
  conduct the practical test. Instead, the inspector will refer the
  matter to the immediate supervisor for resolution. The supervisor may
  need to consult with regional counsel for a determination concerning
  whether the applicant meets the moral character eligibility
  requirement.

That's the basic guidance that the examiners have, but there are also legal cases that have delved into this area and give more specific examples.  I found a blog which covers it in some detail at All About Airplanes.  Falsification of documents, embezzlement, and acting in a malicious manner towards others are cited as reasons that ATP certificates have been denied or revoked.

Multiple misdemeanor charges were disqualifying for one applicant. I believe that case is still in front of the NTSB.  The last rumor I heard was that writing bad checks and larceny may not result in denial. However multiple charges of domestic violence (misdemeanor) were considered disqualifying, however I do not have direct knowledge of that case.

In 1994, four years after he had disposed of the last of his interests in other airlines, the FAA denied Frank Lorenzo an operating certificate for startup airline ATX, saying that Texas Air, Eastern, and Continental "experienced operational, maintenance and labor-related problems that were among the most serious in the history of U.S. aviation."
Loenzo's rejection was described in a New York Times article dated 6 April 1994.
This rejection was not for the ATP certificate, but for an operating certificate (which is issued to the ATP's employer).

To make the answer more complete, is there an article that you can reference?

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text:
Explaining development of sideslip due to bank
In lateral static stability:
"Once an airplane banked due to a disturbance, the airplane develops a sideslip in the direction of the bank because of a spanwise component of the weight w*sin($\phi$)"
I need to understand that in terms of forces and moments acted on the airplane.
Let me say:
the resultan of thrust force and the component of the lift.sin($\phi$) force, which developed when banking, makes the airplane moves in a sideslip angle.
Is it correct?
Can someone explain in it with images?

where does your quote comes from? adding some context may help.

Sideslip is simply lateral movement due to the tilting of the wing lift vector away from vertical. Moving forward while moving laterally means the lateral movement becomes a horizontal arc and becomes a turn.  The vertical fin keeps the body of the plane aligned in the airstream, so the body follows the arc and you have a heading change and a coordinated turn.
You could say the lift force of the wing is a thrust force.  Any time the thrust force is tilted from vertical, the thrust force develops a lateral as well as vertical force component, and because the lateral thrust component decreases the vertical thrust component, the sideslip also introduces a descent.  To stop the descent, you have to increase the total lift to restore the original value of the vertical lift component, so you have to increase angle-of-attack to increase total lift.
Think of a helicopter hovering with the rotor disc level.  All of the rotor's thrust is vertical.  The pilot tilts the rotor with cyclic, tilting the rotor's thrust, introducing a lateral component to the thrust, and the machine moves sideways (and downward because the vertical lift component was reduced, requiring the pilot to increase total rotor thrust with collective), and if it's moving forward instead of hovering while this is going on, the sideways movement becomes an arc, or a turn.
The term sideslip, when applied to flying, tends to refer to the lateral movement without the yawing motion induced by the fin, so that the airplane is turning, but slewing sideways while doing so, and the fin's job is to stop the slewing by weathervaning the tail to keep the body aligned in the relative airflow.
Problem is, dihedral effect requires this sideways slewing to be present when the airplane banks, so that the differential lift created by the slewing motion (sideslip) provides a restorative righting moment.  A small amount of sideslip must be permitted to happen when the airplane is banked by a disturbance to allow dihedral effect to work, but not too much, and not too little.
Vertical fin sizing has to find the sweet spot where a bit of slip is allowed to develop when the plane is banked by a bump, without letting it get out of hand.  Make the surface too small, and the airplane develops too much slip when banking and generally yaws around too much, make it too big and the plane instantly yaws or weathervanes into the bank to remove the sideslip, dihedral becomes ineffective, and the plane tends to want to always spiral into the bank with any disturbance.


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What material is the B737 wing skin made out of?
What material is the B737 wing skin made out of?
I actually couldn't find much information on the wing skin upper and lower panel materials for the B737, the general guess is of course aluminium, but I'm hoping to know specifically what series of aluminium?
The 2000 or the 7000 series? even within these, specifically which one like, Al 7068 or Al 2124?

Aluminum alloy 7178 on the upper skin
Aluminum alloy 7055 on the lower skin
Here is some technical information


text:
How are composite aircraft canopies constructed that sit flush with the fuselage?

More specifically, how is the composite frame of the canopy manufactured? Attached picture as an example.

It's done with a mold, I'm not sure what you're asking though, do you want to know the molding process?

Yes! How to make the joggle on the fuselage that receives the canopy and the canopy frame that sits in it.

That is a complicated process. You need:

A positive mold (mandrel) for the canopy.
A negative mold for the canopy frame. For a single prototype you can also use the unfinished fuselage itself.
A fuselage mold with a molded window sill.

First the fuselage positive mold core is built. From that the negative mold is taken, but also a negative mold only for the canopy area. From that negative mold the mandrel for canopy manufacture is built. If you have enough money, you can of course CNC mill the mandrel directly from a large block of aluminium.
The plexiglass canopy is deep-drawn over this mandrel by the canopy manufacturer, e.g. Mecaplex. There aren't many who get this process right!
Meanwhile, the window sill has been added to the fuselage mold and can be used for manufacturing the canopy frame mold. Once that is finished, the canopy frame is built by first lining the mold with diagonal weave fabric (glass or carbon, as you like) and filling the core of the frame with unidirectional rovings. Then another couple of diagonal weave layers is added on top. After removal from the mold the frame is trimmed and now the transparent part is added. The frame has a recess where the plexiglass fits in and the plexiglass is fixed to the frame with a special polyurethane adhesive. A couple of screws make sure it stays in the correct location.
To finish the canopy, the fittings are added and the frame is painted.

The canopy frame on my PL-2 is f-glass built over steel tubing, with the f-glass joggled around the perimeter to accept the moulded plexi flush, but the builder attached it with screws through the plexi into drilled and tapped holes right in the epoxy matrix.They were leading to hole cracks and bits of the edge of the plexi breaking off and after I repaired the plexi I thot of replacing the screws with that polyur glue like the RV guys do,but instead just enlarged the plexi holes and installed the screws with large c-sunk washers so there are no lateral forces on the holes. No problems so far.

Peter Kämpf, the last paragraph is where I'm having difficulties. How exactly did we move from a  solid mold to a mold with window sills? I know that a tool is attached to the fuselage molds to get that joggle, but I can't think of a way to manufacture of the pattern for the tool other than CNC.

@Mridul It's a long time since I did it, so I'm no longer exactly sure. One way would be to cut the profile of the frame in high density styrofoam with a hot wire and bend that strip into shape and fix it to the fuselage mold, then cover it with packaging tape. But that was for a prototype, so serial production would use a layer of glassfiber and filler for a smooth surface instead.

@JohnK The cracks emanating from the screws is a known problem. The trick is to not tighten the screws all the way so the plexiglass is not compressed by the screw head. And countersink liberally, so the screw head does not stick out a bit.


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Should composite ribs be made in the same way as metal ones?
A lot of metal ribs are made from bending or stamping sheet metals. So we see shapes which have lots of discontinuities in the flange area for ease in manufacturing. My question is - is it the most ideal shape for a rib keeping manufacturing ease and stringer requirements aside? In an aircraft with carbon fibre sandwich skin, would ribs with complete flanges be more suitable?

vs

Should composite ribs be made in the same way as metal ones?

No
Doing so would forfeit some of the benefits of composites, but certification authorities and their regulations might force you to.
To start, it is important to understand what the rib is for. Most have several purposes:

Carry lift forces from the nose and rear part of the airfoil to the spar.
Keep the wing skin in shape and prevent buckling.
Support bearings for control rods, cables or actuators.
Introduce point loads into the wing, say at an engine mount or a landing gear leg attachment.

1 and 4 mean that the rib is like a small spar in itself: The upper and lower flange are loaded in tension rsp. compression and the rib area itself carries shear forces. This translates into unidirectional fibers along the flange and ±45° woven fibers of lower stiffness for the area in between.
Generally, it is better to reduce wall thickness instead of using cutouts to reduce weight, but the resulting thickness could make the rib prone to buckling. Therefore, it can be optimal to use a corrugation or sandwich in the shear loaded parts and 3 could make cutouts necessary. Fuel passages in a wet wing should be kept small to avoid excessive sloshing. As a rule of thumb, add as much fiber mass around the cutout as has been removed.
Discontinuities in the flange area would be a stupid mistake in composite construction since the wing skin is most likely a sandwich panel without stringers running across.
And now we need to placate the authorities: This could mean that the rib is not bonded, but riveted to the wing skin in order to allow later removal for inspection or repair. Never mind that it will be easier to repair a composite structure by grinding away the damaged parts and replacing them with an adequate layup, but a century of bad experiences with metals have condensed into some very specific rules which demand that you use composites as black aluminium. Next, instead of a sandwich the wing skin might consist of a solid sheet stiffened by discrete stringers. In that case, you would first bond the unidirectional fibers on the inner skin before adding the stringers and the rib area with those cutouts you show in your metal rib picture.

The cuts in the metal ribs serve several purposes:

They accommodate the need of the metal to bunch up or wrinkle as the
flange is formed around a curved form block (because the edge of the
metal is being forced to shorten in the forming process). The relief cutouts make the rib easiest to form, at the cost of some strength.
They provide a secondary use in making room for stringers, lateral stiffeners, or machined flanges in a milled wing plank.
They provide a fuel path if the wing is "wet" so fuel in the outboard end can flow to the inboard end past the ribs.

If you don't need the stringer cutouts and it's not a wet wing, an alternative to the flange relief cutouts is to form indentations along a continuous flange, called flutes, to take up the excess metal that is created in the forming process. You can avoid cutouts or flutes completely in a metal rib, but you have to form the rib in a dead soft annealed state, and heat treat it after forming.
For a composite rib made in a mould, you would only use cutouts or slots along the flange to accommodate lateral stiffeners in the composite skin, or for fuel passage in a wet wing. A composite skin that is flat on its inside surface would have no need for flange relief cutouts for that purpose, and if there isn't any fuel, it wouldn't need fuel openings either.


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How do engineers estimate the aerodynamic effects caused by jet engines or propellers in wind tunnels?
When aircraft models are tested in wind tunnels they don't seem to have engines or propellors on them. So how do engineers get correct parameters from the experiments? Do they just seal the air inlets where jet engine is supposed to be?
Similar question, how is it done in computer simulations?

A400M tested with engines and propellers, It's not usual, the reasons are explained in the document. There are even engine simulators.

Turbofan and propeller thrust is known from the manufacturer and does not normally need to be included in wind tunnel testing. Models usually represent solid structure, so they have:
hollow nacelles

propellers left off

However, Cessna included props with electric motors on their Sky Courier tests.

In CFD models can exclude engines as well, but there is also the option of adding an "actuator disc" where energy is added to the airstream that flows through the disc. Swirl can be added to the stream through propellers if that is the purpose of the simulation, but this does not normally have a large effect.


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Is the property of having a neutral point (aerodynamic centre) specific to an airfoil shape or will every arbitrary shape will have one?
Is the property of having a neutral point (aerodynamic centre) specific to an airfoil shape or will every arbitrary shape will have one?
Asking in mostly context of fuselages.

In general I'd say no. Just think about a non-rotating ball for example: it definitely has no lift nor pitching moment, only drag; so it doesn't have any aerodynamic center. I suppose that the same reasoning apply as well to any body with some symmetry.

@sophit curious in the case where a sphere is dropped straight down.  There was one video where (an offcentered) ball was dropped from a great height, and it started going Magnus effect.

That is an interesting question.  I'll say right away -- I don't know, but I think we can think our way through this.
The fact that an airfoil has an aerodynamic center (a point around which the moment does not vary) -- and that the location of the ac is c/4 -- and our ability to calculate that moment all come from thin airfoil theory.
We can of course use more complex theories to see these things, but the most simple theory that analytically shows these things is thin airfoil theory.  TAF is based on inviscid, incompressible, 2D flow.
So, it is natural to look at an inviscid, incompressible, 2D flow theory on a non-airfoil body to answer your question.
One fact about this flow model is that the flow will always be attached.
The big difference between a non-airfoil body and an airfoil is that we won't have a sharp trailing edge on the body.  I.e. we will not apply a Kutta condition.
This means that the non-airfoil body will not support any lift (it will still have moments, but no forces).  I know it sounds crazy, but it is true -- in this flow model, a body will not have any lift or drag.
Without enforcing the Kutta condition at the sharp trailing edge, the rear stagnation point will move until it 'finds' the no-load point.  If you force separation anywhere else, you will get forces -- but it naturally will find the no-force solution.
So, this means our body has a moment about it, but no forces.
If the body is symmetrical, then at zero alpha, it will have zero moment. However, at some non-zero alpha, it will have non-zero moment.  So -- the moment changes with angle of attack.
Since there is no force (to contribute to the moment depending on the moment arm), we know that this is a pure couple -- and it will be the same no matter the reference point for moments.
So, we'll have a non-zero moment that varies with alpha, no matter the location of the moment reference point.
So, no -- non-lifting bodies do not have an aerodynamic center the way airfoils do.
I know everything I've said in this post about non-lifting bodies in potential flow also applies to 3D flow.
I'm comfortable with the incompressible restriction -- the answer could well be different in compressible or supersonic flow, but this discussion should hold true for a lot of subsonic flows.
The big question is the inviscid assumption.  Real flows have viscosity.  In those flows, the adverse pressure gradient on the aft side of the blunt body determines where the flow separates.  This locates the aft stagnation point and can allow the body to have lift.  You must be very gentle to allow the flow to find the no-force solution with a real boundary layer.
This blunt-body separation problem is a very challenging problem of aerodynamics.  It is hard to study in a wind tunnel because we usually place bodies on a sting mount -- but the sting itself changes the flow in this region.
Blunt bodies like fuselages end up having separation points that move with angle of attack -- and are hard to predict.
So, if you had a fuselage with a feature on the aft side (sharp TE, strakes, flat blunt end, etc) that forced the flow to separate at a consistent location -- then I think it might have an aerodynamic center.
However, if the aft separation point is allowed to move around (reaching the no-load solution, or just wandering a bit depending on alpha), then I do not think you will it behave like it has an aerodynamic center.

Although I am not challenging the utility of neutral point calculation for a given configuration. But a neutral point, as we know wrt airfoils should not exist for an aircraft with a fuselage? Say an aircraft with low aspect ratio wings where fuselage moments have significant contribution

I suspect that the fuselage contribution is seldom significant when compared with that of the horizontal tail -- a lifting surface on a moment arm produces a much larger moment than the cm0 of the wing or tail.  I suspect the effect you're thinking of exists, but isn't very important.

Yes, any shape will have a neutral point, the trick is to find it and use it for pitch stability design.

The neutral point is where angle of attack does not affect pitching moment.

Does a sphere have a neutral point?  Sure.  Right in the middle.

But as always, aviation would be easy if there was no air.

Lifting efficiency and distribution of certain shapes can affect center of pressure, depending on angle of attack, which can affect (pitching and yawing) stability characteristics of an airfoil and/or fuselage.
One of the primary jobs of the tail is to counter-act the forward movement of center of pressure with a cambered airfoil as AoA increases$^1$.
Designers, furthermore, can place the center of gravity further forward of the AC and add some downforce to the tail, increasing longitudinal stability$^2$ and introducing static stability$^3$.
In the end AC is a nuetral pitch stability concept, but behavior of all aerodynamic shapes must be evaluated.
$^1$ symmetrical airfoils do not have this issue
$^2$ ranging from trainers to highly unstable computer controlled aircraft
$^3$ yes, a lifting tail can be staticly stable, but if weight is moved forward, whatever the original (tail) lifting condition, tail lift must be reduced.


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What causes air flow towards fuselage near the winglet?
I am trying to understand how winglets are beneficial in reducing induced drag and I came across this article;
https://www.boldmethod.com/learn-to-fly/aerodynamics/how-winglets-work-to-reduce-drag-and-how-wingtip-vortices-form/
In the context of the above article, The component of velocity towards should be towards the fuselage when a vortex is shed at the tip with no winglet. But by adding a winglet the vortex would be shed at the winglet's tip and the velocity component seen by the winglet should be away from the fuselage. Can some give me an insight into what really is happening?
Is the explanation that winglets actually produce negative drag true?

The winglet is working like a sail on a boat close hauled on a tack; most of the lift is sideways, but there is a small forward thrust component that drives the boat forward, and the winglet gives enough forward thrust to exceed its drag at high AOAs. This is why they are only seen, mostly, on high altitude jets that cruise at low indicated speed.  There is also the winglet's outwash, redirecting the vortice field in the opposite direction, weakening the circulation.  Stand under a winglet and you might notice its chord line is toed out a bit, to optimize its AOA into the local circulation.

@JohnK I have been doing some reading and there seems to be some debate regarding winglets behaving like sails. Although I haven't been able to find any satisfactory theory suggesting other methods of their working.

Note the expansion of my answer. I hope this helps to support @JohnK's reasoning.

Suction does.
Air flow follows pressure gradients, and the lift-creating suction over the upper wing pulls in more air, not only from ahead of the airplane (which explains the induced angle of attack), but also from the side.
The explanation of induced drag on the Boldmethod page is actually quite good; only gems like the wingtip vortices curve up and around the wingtips, pushing the air flowing over the wing downward and the graph with straight arrows on a swept wing are in need of improvement.
The better wording would be: Lift is created by accelerating the air flowing over the wing downward; this in turn causes more air from the side to be accelerated towards the center of the wing.
Regarding the comparison of winglets to sails: The sideways acceleration of the air near the tip causes an inward-bent airflow above the wingtip. If you now place a sideforce-creating surface there, its lift vector will be tilted forward by this inward-bent airflow. This will produce a small thrust component together with a large side force, just like a sail does when sailing close to the wind.
This effect works in the same way as the downward-bent flow over the wing which causes the wing's lift vector to be bent slightly backwards, causing induced drag. You might, therefore, call the beneficial effect of the winglet induced thrust. Just like induced drag, it is biggest at high lift coefficients.
Of course, folding this winglet flat out as a span extension will be even more beneficial.

Thanks Mr. Kampf. Am I right in deducing that in all these cases the major part of vortex is still being shed at the wingtip and not the tip of winglet.

There is a large flow field circulating around the wing tip extending out well beyond the winglet's own length, weakening as you get farther away.  The winglet is just extracting energy from the strongest core section of the circulation to help weaken it and get a bit of thrust benefit from it. Whitcomb's objective with the winglet was to get the benefit of a span increase without the actual additional spanwise space taken up and without the added bending load on the spar root, since the winglet's structural impact is absorbed at the base of the winglet and doesn't add to overall wing bending.

The best article on winglets I've ever seen was a Peter Garrison (who designed his own aircraft and flew around he world with it) article in FLYING magazine many years ago where he describes it perfectly in lay terms.

@Mridul Vorticity is shed along the whole span and rolls up into the two vortices. What happens at the tip is only a minor part of the whole.

I guess you could say the wing itself is one big vortex generator, a delta wing being the most extreme version.


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Why are W, S, N, E highlighted on a flight management computer?
Why are W, S, N, E highlighted on a flight management computer (FMC)? My assumption that they represent West, South, North, and East.
Here is a Boeing FMC:

And here is one from Airbus:

Correct. North, South, East, West when dealing with longitude and latitude, e.g. creating a waypoint or entering the current position for inertial alignment (the second image).

A good question indeed, it's easy to say that it represents the four directions, but why it's done is something else. Whats so time-critical to have those buttons highlighted?

@NoahKrasser: The only key used when entering coordinates are the rounded numeric keys and these 4 letters, that's enough to make them look different.

N, E, S, W is definitely used for entering lat/long coordinates. On the Airbus graphic in the question, you can see the pilot has entered their starting latitude and longitude with N and W.
But why are they highlighted? I'm going to guess and say it has to do with the transition between old-style numeric nav computers and "modern" FMS. Old style IRS only had a numeric keypad like this Concorde unit:

(Source)
and you can see that N, E, S, W is entered on the 2, 6, 8, 4 keys. So instead of typing "3253.9N" on the CDU you'd hit "325392". You'll still find these numeric keypads today on some forgotten corner of the overhead panel for who knows why, even on a 777.
I think the squares are a cue for the old time pilots that you can't enter a N coordinate by hitting 2, you have to hit the N key, and it also helps them find it.

The highlighted keys denotes the four directions, as mins has mentioned.
I could not find more information about this other than this:

Placement of the letter designator (N, S, E, W) in the string of five
  characters indicates the value of the longitude one-hundredths digit

The letter in the last position indicates longitude is less than 100
The letter in the third position indicates longitude is 100 or greater

For Example:
Letter   Lat     Lon
N        North   West
E        North   East
S        South   East
W        South   West

PPrune also said the same.


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What are mechanical requirements for flying over water?
What are the mechanical requirements to fly over a large water body? Are multiple engines required? Do the engine/s need to be a certain kind (turbofan, turboprop, piston)?

Are you asking from a commercial operations standpoint, or private? Are you wondering about equipment requirements? I'm not sure what "mechanical" requirements are. How long would they be over water? How far offshore are they travelling?

The mechanical requirements are the same as for flying over land - if it flies, it doesn't matter what's down below.  Single-engine prop planes regularly cross the Atlantic (see ferry flights), and have done so since Lindberg. Perhaps you are asking about regulatory requirements?

Private operations - no requirements. Single-engine is legal, you can argue as to the safety.
Commercial operations...
Single-engine: within gliding distance of the land.
Twin-engines: always within 60 minutes of the land... unless specially approved airplane and operator, and airplane maintained according to much higher specs - this is ETOPS.
More-than-two engines: no problem.


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What is the difference between a go-around and a missed approach?
What is the difference between a go-around and a missed approach? What are the steps involved in each of the procedures?

Approach, missed approach, departure & holding
Approach, missed approach, departure and holding are published instrument procedures. They are characterised by waypoints, alitudes, headings, climb-, and descend profiles.
An approach procedure tells you how to get from cruise to short final, from a holding to short final, or from cruise into a holding.
A missed approach procedure tells you how to get from climb out into a holding or to another point from where you can commence a new approach.
A departure procedure tells you how to get from climb out to cruise flight.
Takeoff, landing, go around & touch and go
Landing is the process of getting an aircraft from short final to a full stop on the runway.
Takeoff is the process of getting an aircraft from a full stop to climb out.
A go around takes an aircraft from short final to climb out directly, not touching the runway.
A touch and go takes the aircraft from short final to climb out, touching the runway in the process.
Relationships
The procedures listed above can be combined arbitrarily. Even though a missed approach is often flown after a go around, they are not synonymous. Missed approaches can also be (and are) flown after a touch and go, or, for training purposes, after a takeoff. Also, a missed approach is not the only thing you can follow after a go around: Sometimes, you want to perform a departure and continue toward your alternate destination.

A go around is terminology generally used during VFR flight. If a pilot is approaching the runway to land and decides that conditions are not conducive to a safe landing, he can opt to “go around”. This can be for a wide variety of reasons including the pilot or aircraft being unprepared for the landing, the descent to landing being performed poorly, or even animals/FOD on the runway.
In a go around, the pilot will first apply power, then “clean up” by retracting flaps/gear as necessary to reduce drag (down to 20 degrees in a C172). Once a positive rate of climb has been established, the pilot will remove the remaining flaps and radio that he is going around. Generally the pilot will re-enter the traffic pattern and attempt to land again.
A missed approach is terminology used exclusively with instrument approaches. Instrument approaches always have a missed approach procedure in case the pilot is unable to complete the approach. This most often happens when cloud cover and visibility are poorer than allowed by the approach. If a pilot descends to a certain altitude and is unable to see the landing environment or at least the airport lights, he will “clean up” similarly to the go around procedure discussed above, tell ATC that they have “gone missed” and then follow the steps outlined on the instrument approach plate.  These steps generally involve the aircraft climbing to a safe altitude and entering a hold.  At this point the pilot can choose what their next course of action is.
Missed approaches can also be used if the pilot decides that he isn’t well prepared for the approach, and the missed approach procedure must be initiated if the pilot doesn’t stick to the approach closely enough.

You are wrong. Go-around is used in IFR aswell. I have heard ATC instruct aircraft multiple times: "BAW123 Go-Around I say again Go-Around, aknowledge". It is AFTER this instruction that they tell them to follow Standard Missed Approach PROC

I used and bolded the phrase “generally used during VFR flight” on purpose. While I too have heard it used during a landing done after an instrument approach, I think you would agree that while possible, go arounds are much more common during VFR flight.

I am trying to tell you that the Go-Around instruction is used on both IFR and VFR if needed. As far as I know VFR aircraft rarely request a Go-Around, but they frequently request a Touch and Go. Go-Around is used by ATC/Pilots when one side or another decides that it is unsafe to land, and is requested-issued when the aircraft is on final approach. Generally speaking, go arounds are used on IFR as much as VFR.

^CAP 413, Chapter 4 Paragraph 65

Admittedly I’ve only been instrument rated for a year, but I have never been ordered to go around while flying IFR.  I have heard it happen once. Go arounds seem downright common for GA VFR flight. This seems super minor though, so I’ll agree to disagree with you. I am US-based and you appear to be Canadian from your source, maybe there’s some difference we aren’t aware of.

"Go Around"  is used for both VFR and IFR. An IFR pilot will fly the "Missed Approach Procedure" after the "Go Aound" is initiated.

"Go Around" is the ATC instruction used in any circumstances, IFR or VFR, where it is necessary to execute a Missed Approach. There is no instruction such as "make Missed Approach", the instruction is "Go Around".


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How do holding patterns work?
How does a pilot follow a holding pattern? Do pilots have to manually change heading and altitude (through the autopilot) each time they are making a turn? Or is it something the Flight Management Computer (FMC) can handle?

You might need to improve your question. You added air-traffic-control tag in your question but the question body has nothing to do with ATC. Also "How do holding patterns work?" is a very broad title that will call for a variety of answers.

Generally speaking the Flight Management Computer supports holding patterns. The pilot inputs the holding fix (usually a NDB/VOR), the direction of the hold (Left/Right), the inbound course, and the time/distance that one holding leg shall take to execute. These information can be found on aeronautical charts, as IFR holding patterns are published for each airport. As far as I know pilots are also trained to fly holding patterns manually, but you can understand that flying the pattern manually is not as precise as flying the pattern via the autopilot.


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When is a steep takeoff appropriate?
There are plenty of videos of aircraft performing "steep" takeoffs, such as this one. When, if ever, is this kind of takeoff appropriate. What is the procedure?

air show is definitely one of those occasions

The short answer is, when the surrounding environment requires it. The procedure here is perhaps most akin to a short field take off over a 50 ft obstacle but a few things are going on. The aircraft, as soon as it leaves the ground is climbing at Vx which allows for the maximum angle of climb.

Vx is the speed for best angle of climb while Vy is the speed for best
  rate of climb.

In your linked video its mostly for show. In practice short field over a 50ft obstacle takeoffs are used for, well, short fields... or when you need to get off the ground fast so as to get over some obstacle at the end of the runway. Generally speaking most commercial airports have long runways that are more or less obstacle free (with some notable exceptions) so short field maneuvers are not what they are in general aviation. There are lots of small fields all over the country that have trees (also known as 50 foot obstacles) power lines, buildings, church steeples or any manner of obstacle at the end of the runway. On top of that many of these strips are on the shorter side (under 3000 ft.) so you simply have less runway to work with and your margins can be far smaller. In this case you want to get off the ground as soon as possibly and climb as fast as possible.
It is the pilots responsibility to operate the aircraft safely and these kinds of maneuvers are well within operating limitations. In small planes they happen more often than you would think, especially if operating out of a short strip. and even us lowly private pilots are trained in short field 50ft obstacle clearance maneuvers. As for the big guys if the airport environment calls for it, it may be performed but I would think it is less common as most commercial airliners can pitch up far more than people in the back would be happy with. Someone with more commercial experience may be able to elaborate on how often they happen in practice there.
There are a few things to keep in mind as well, military planes simply have a much higher thrust to weight ratio than commercial airliners and can in some cases sustain vertical climb outs. Military jets also often have afterburners for an added boost. The commercial planes you see in the linked video are more than likely lightly loaded carrying only a partial fuel load. Camera angles can also make it look as though the plane is climbing much steeper than it really is.

I think you mean Vx - maximum angle of climb. Most normal takeoffs/climbs are at Vy and are not as spectacular.

@Ben my mistake, I have updated to reflect.


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Is a holding pattern always counter-clockwise?
Is a holding pattern always counter-clockwise? Or is it dependent upon the controlling airspace?

Right turns are standard for ICAO. In PANS-OPS (Doc 8168), Procedures for Air Navigation Services, section 4, chapter 1: "If no operational considerations prevail, right turns holding patterns should be established. For left turns holding patterns, the corresponding entry and holding procedures are symmetrical with respect to the inbound holding track"

No. The holding pattern can have any inbound course, and any direction. The holding pattern course/direction, depends on departing/arriving traffic, and many other factors. London Heathrow has a clockwise and counterclockwise hold on the fix LYDD.
Thanks to Pondlife for pointing LYDD out!

A better example from your image might be the holds at LYDD: one uses right turns and the other uses left turns.

You could use both patterns, do a figure-8 and not get dizzy!  :)


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What simulation software do airlines use?
What simulation software do airlines use for training purposes? Do they use software like P3D, FSX, X-Plane, or FlightGear? Or is it a custom? What about aircraft? Do they source them from groups like PMDG or is this also custom?

Flight schools do not use computer games for training, they use professional software

For general aviation, search for PCATD. For larger aircraft, it's a full fledge flight simulator or flight training device, http://www.cae.com/civil-aviation/training-equipment/flight-training-devices/

@J.Hougaard Most of the "computer games" are professional software... the only difference being license terms and any customizations put on top and usually full-motion systems and/or complete cockpit mockups. If every training simulator company completely re-invented the wheel, they'd never be profitable. So much development goes into flight modeling, physics, etc... Flight sim software sold to "regular people" increases the userbase of the software, which helps shake out bugs (and fund improvements) a lot faster than if it were only companies using the software.

Folks, the OP is asking about the software - of course the hardware for a full-motion flight sim is very expensive, but these companies that are being cited are unlikely writing their own in-house simulation software - it's more likely a modified commercially available FAA approved flight simulation.

@SnakeDoc I gave ample evidence in my answer that it's not commercial software at all. It's custom software using models provided by the aircraft manufacturer, code from taken from actual avionics and real flight hardware. Just look at the hardware on the actual FFS I linked. Since when did these programs run on an IBM RS/6000?

@user71659 Since an IBM RS/6000 is a RISC CPU architecture based UNIX server, it can run just about any normal software, X-Plane included (which is designed to run on UNIX environments). Yes, they make custom models, but the core software is going to be something another company developed... such as X-Plane or P3D. Wasting time and money developing a core simulator again would be a massive misappropriation of resources, and it's unlikely you're going to convince Boeing et al to spend a lot of their time re-developing the same aircraft model for some random home-brewed simulator.

@user71659 Look, I know you folks like to think you're using some real special gear when using these big commercial flight simulations -- and you are, the hardware and customizations are certainly special... but the core simulator is a commercially licensed version of an FAA certified simulator like X-Plane or Prepar3d. They start with a good quality base, and build on top of it. It's literally the entire reason Prepar3d (and before it ESP) and Commercial X-Plane exist.

@SnakeDoc Nope. They do have reusable software like Rockwell Colins  CORE. The reason why you can't use PC software like X-Plane is both hard latency requirements (as discussed in the last article I linked), and the fact that you need to interface to external hardware. If you read the Linux article, it explains that the point of the sim software is to interface between hardware and software modules provided by different vendors.

Furthermore: When e.g. aerospace engineers use something like OpenFOAM or (shriek) Linux for their aerodynamics computations, or Python to evaluate big datesets, does it make them non-professional? I think it's best to just ditch the term "professional" from the list of arguments; it's way tooambiguous.

A very big helicopter company where my friend works has a sister-company that only makes simulator for their products, collaborating with the dynamics team of the "real thing". Those sims are more expensive that the actual hely!

@Caterpillaraoz Well the pricing on highly specialized equipment (aka a simulator for one specific type of aircraft) is likely very expensive because development costs are high and overall sales are low. That doesn't say anything about how good or bad a software emulates flight physics and the behaviour of an airplane. The problem is not in the software but for training use it must be able to simulate the aircraft also in the hardware, including response times to controls etc. Validation is the costly part, so you can be sure it behaves accurately for the intended training exercise.

See also, but not a duplicate: Can Microsoft Flight Simulator help me learn to fly (or make me a better pilot)?

X-Plane offers a "Professional Level" which is mostly about licensing. However X-Plane also has an FAA certified version that if paired with proper controls is legal for certain training/instructional hours. You can find more info on the FAA's approved simulators here and here. The flight school I trained at had a certified sim from the 80's that was pretty miserable by todays standards. It was certified and had no screen, I would say it was "custom built" FWIW.
Many airlines may turn back to the manufacturer for recurrent training. Both Boeing and Airbus run facilities with full motion simulators. I would think they built the software in-house but I don't have any hard evidence on that. As the OEM builder they have access to genuine interior parts to build the sims.
For smaller aircraft places like SIMCOM offer training in full motion sims but do not list their software of choice. SIMCOM uses actual aircraft interiors (most likely from defunct airframes) for their sims.
If your really adventurous you can build a full cockpit sim yourself.

Boeing makes military aircraft, I'd bet they've got an in-house simulator.

@Carl Lockheed Martin bought ESP from Microsoft (the commercial version of FSX), and it's released as Prepar3d (P3D) to the public and for commercial applications. Lockheed did this so that they had a solid simulator platform, and didn't have to spend all the time and money building one from scratch - they specialize in building aircraft after all, not simulators. I doubt Boeing homebrewed their own simulator, it would be a huge waste of time and money.

@SnakeDoc The first flight simulator was funded by the military and it's the reason we store data on magnets.  The pilots who first flew the F-35 knew how to fly it before it was built.  Yeah, LM makes planes, but the reason they are good planes is because the simulation behind them.  I highly doubt that Microsoft had anything to offer LM other than a code-base that was not 100% ultra-top-secret.

@Dave worth adding to compliment your answer: https://aviation.stackexchange.com/questions/12634/how-close-is-x-plane-experience-to-real-flying?rq=1

Computer games try to model the aircraft based on generalized aerodynamic and physical principles and at best "feel". FAA and EASA certified full flight simulators are built with a data package purchased from the airframer, which uses their developmental models coupled with actual flight test data.
On top of that, full flight simulators do not simulate much of the hardware. Things like FMS, display computers, autopilot, and even fly-by-wire computers, are traditionally done with actual flight hardware that are fed with data from the simulator. This ensures the highest levels of fidelity. In newer systems, if they don't run the hardware, they obtain the original code from the vendors and run it in a software simulator (a process called re-hosting).
Obviously none of the enthusiast programs can do this. A single full flight simulator can cost up to $20 Million, so their resources are far better than what enthusiast software program can do. For full-size jets, there are essentially two companies in the world who do this, CAE and L-3 CTS (formerly Thales).
Here's a (somewhat older) article detailing the custom software architecture these simulators use.

18 years ago? That is ancient

@Koyovis Not as ancient as if you need to train on a plane like a 727. You'll be using a MicroVAX. I had to look up what a GP-4 was!

This is not entirely correct, enthusiast programs like X-Plane (and to an extent FSX) have GPS, Autopilot, and FMS systems modeled in and fully functional. While not pure hardware implementations like the real thing the simulated outcome is for all practical purposes the same.

@Dave No it isn't. First, show me a FMS simulator in X-Plane that can do FLS (FMS Landing System, Boeing IAN). How about a RNP AR approach? The second critical part is failures. 75% of sim flying is failures and modeling cascading failures accurately is critical. What happens if you're on an autoland and AC BUS 2 fails. Or a FMGC1 major reset, what are the cockpit effects? How do you use backup nav mode? Remember, the first time pilots who are trained on a FAA Level D Simulator touch a plane, it has passengers on it. Even the cockpit lights on a FFS are modeled into the correct buses.

This is an example of a standard FFS failure drill. Note the depth of failures that are modeled, displays fail, lights fail, standby instruments go off, flight controls degrade, autopilot fails... The realism down to how long it takes for the displays to reconfigure... because they're using real display computers.

@user71659 You're missing the point. They start with something like X-Plane, and then build on top of it - in both custom modules (software), custom models (software), and custom hardware such as cockpits, full motion, etc. Just because joe-shmo can't buy a 100% accurate 747 model in X-Plane for $34.99 doesn't mean a big professional simulator company with direct collaboration with Boeing cannot build such a thing on top of the platform. This is what they do... they spend countless hours building the models... but not the core sim. That would be a fools errand and a waste of resources.

building the models?  building 3D models is nothing.  it takes a couple minimum wage workers - a non-issue.  you can engineer a basic flight simulator using any common game engine in a matter of a week or two (obviously it takes longer to make a "good" flight simulator, just as GT3 takes longer to make than an everyday car game).  every single point that user71659 makes is completely correct, of course.

the confusion on this page is like confusing the overall software system that runs your bank with an (excellent) desktop software product that deals with numbers, such as Excel.

@Fattie models, in the context of flight sims, means a whole lot more than some skins and shapes. Everything about a particular aircraft is included in the "model". FMC, systems, gauges, handling characteristics, flight model, etc. It's not the same as you're comparison. Some models take years to develop and make accurate.

Yes the PC software that OP mentions can be used for professional flight training - if it demonstrates to the authorities that it matches aircraft data, and that is where the distinction lies. It has to be FAA/EASA qualified, where EASA has stricter rules on low level devices.
The distinction between computer games and flight simulators has been blurring in the last decade. What's the difference anyway, on a PC we see an out-the-window view, a 6-DoF model of an aeroplane react to our inputs, hear sounds, can see indicators move...walks like a duck, quacks like a duck, must be a duck, right?
Not necessarily. The main difference is the verification. A computer program sold to the general public does not have to prove to anybody that the model behaves like the real aeroplane, just manage feedback from users. A simulation device used for professional training, does have to demonstrate fidelity: the FAA and EASA want you to objectively prove how realistic the device is. So whatever software you use (and it can be X-plane or FlightGear) must demonstrate that it matches objective aircraft measurements.
Building flight simulators used to be akin to black magic. 30 years ago, building a Level D simulator was an almost impossible feat of engineering, a brilliant effort to reproduce all failures modes that pilots are trained for handling, running on multiple Super Fast processors in a Unix environment. Super Fast meaning about 286-type performance, with zero MB memory. The Level D fully justified a high price.

Not anymore. Yes the hardware is not cheap, but with today's sales prices less than half the price of a Level D simulator. Robotics and fast processors have made the hardware cost pretty reasonable nowadays, and there have been market disruptors (disclaimer: I used to sell their devices). Nowadays the main cost of a Level D simulator is in the license price that needs to be paid to the aircraft manufacturers for use of their data.
Whose software is running on the devices?

Airbus and now Boeing have started to deliver black boxes with the flight model running on it, together with the license.
All major manufacturers have developed their own flight model software in the past. A major effort (> 100 man years) because there are so many aircraft response plots to match, and only six degrees of freedom. CAE, TRU, FlightSafety, Indra, Axis, L-3 have delivered Level D simulators with in house developed software models and verified flight model responses.
Some research institutes have delivered simulator flight models. NLR of The Netherlands has delivered a Level-C helicopter flight model for KARi for instance.
Some manufacturers who pioneered low cost, low level Flight Training Devices such as Frasca have delivered full motion simulators.

There are new kids on the block as well, a company like RedBird is taking a blank slate approach. A GA type cockpit inside. This type of simulator is FAA approved, for a lower standard than the Letter Devices, of which mostly Level D is now delivered.
The PC software that OP mentions can be used for flight training, and make very good practising tools for standard operations: power up the aircraft, start all systems, start the engines, learn how to trim, how to operate the radio, how to communicate etc. FLightSim, X-Plane, FlightGear etc are all very useful tools, much more so than the old fashioned way.

Regarding realism, try this: Take your favorite computer-software flight simulator (Microsoft Flight Simulator, Flightgear, X-Plane, ..., whichever), take off normally, and then do something really, really stupid. I took (admittedly a somewhat old) Flightgear's Piper PA-28 for a ride a few days ago, took it to something like 1000-1500 feet, and then pointed the nose essentially straight down and pushed the throttle to maximum. The aircraft actually bounced off the ground! That's how good the flight dynamics model is. I'm pretty sure that would cause a FAA/EASA/etc certification fail.

Yes. I've tried a couple of helicopters and found them to be flying like fixed wing aircraft. You cannot feel accelerations, have no force feedback and usually have no peripheral vision on the PC games, so cannot really tell how realistically it is behaving anyway.

I figure plain computer flight simulators running on commodity hardware have their place, but that place is not serious training for actual flight, especially outside of mostly stable and level flight (as, I think, is so aptly illustrated by that CFIT PA-28 example above).

@MichaelKjörling That's actually an issue with FFS that has lead to fatal accidents. Certification requires the model be backed up by real data and subjective experience from flight tests. The major issue was with stalls and stall recovery. There were explicit instructions not to train past a stall warning because the models were not validated and in many cases invalid for effects like vibration. The lack of training was a causal factors in accidents like AF447, so you can see a lot of simulators are being retrofit due to new FAA requirements to train to a full stall (AC 120-109).

MPS is a relative new company that offers fixed base simulators, I visited their production site a couple of times. IIRCuse a datapack from the aircraft manufacturer, but implement most of the software themselves. I think their visualisation is 3rd party, but the rest is developed in-house. Also note that whilst the flight dynamics is essential for a good flight simulator, a large part of the simulator software deals with the aircraft systems and all possible failures and effects that are associated with that.

@Michael X-plane actually implements a full, realistic, aerodynamic model, though this is uncommon compared to other flight simulator games. Probably this is why X-plane has been used to create some FAA certified simulators (as referenced in other comments) as opposed to other "games".

@mbrig the aerodynamic model of X-plane is simplified (laminar flow, no interferences).

Airliners train their pilots using flight training devices (simulators) to keep them current with their licenses.
"Simulators" range from single PC applications for procedural training to Full Flight Simulators, those that have a realistic cockpit, and that even moves, vibrates and generates the required realistic ambiance (sounds, visuals) to make you feel you are really flying.
The full flight simulators, if certified to Level D, meet strict criteria for simulating a flight condition. From taxi to emergencies and landing in various weather and aircraft conditions. Because of this realism and high fidelity, a flight hour in the simulator is logged into the pilots logbook just like a real flight.
Therefore the simulators that are used for pilot training have complex hardware and software that are developed especially for the particular aircraft they represent.
Here are two links to companies that work in this field:
HAVELSAN
CAE

I worked on D class simulators in Australia and all the software we used was built in house specifically for the task.
For lower fidelity simulations we used a mix of X-plane for aerodynamics and visuals, VBS for the simulation environment and other in house software for instrumentation and other components.
The reason we couldn't use game software like X-plane for D class simulations is because their physics and visual simulations were not up to FAA standard, for example, reflections off of waves in water, flight model oddities in wind conditions and various other environmental shortcuts that are 'good enough' for games but not for simulation purposes.
For the D level simulations, our calculation software had to run at 1000Hz to be as responsive as possible to pilot and environment actions, which (as far as i know) game engines do not support.
If you want some more information here's the public documentation for a couple which use custom software for simulation and display. The documents are a bit basic but they get the general idea across.
Wedgetail simulation
787 simulator
Helicopter trainer

Thales sold its civil simulator business to L3 Link in 2012

Indeed they did. I was around when it happened. Though that just means they use the same technology now.

Commercial carriers use hardware simulators, not software. Each carrier has one or more training facilities. For example, American Airlines has one in Fort Worth and one in Charlotte. Pilots have to learn a wide range of different skills which are not only how to fly particular planes but how to deal with specific types of dangerous situations and ancillary needs such as learning how to perform CPR.
Simulators are generally provided by the aircraft manufacturer and come in two basic types: systems simulators and full-motion simulators. A systems simulator has no visuals, just controls. The pilot learns how to push buttons and perform procedures in the right sequence. The full-motion simulator is a large box on hydraulic mounts that has a visual screens and can tilt in any direction. It is used for training maneuvers.

Hardware simulators still have to run some kind of software though, right?

@ZachLipton Yes, but they run custom software designed specially for the simulator to model the intended aircraft, not retail shrink wrap simulators like X9.


text:
What are SIDS and STARs?
I’ve been exploring the FMC(flight management computer) on the PMDG 777 and noticed that under the route section you can insert VIA and TO points. From what I’ve learnt this is where you would insert SIDs and STARs. What are SIDs and STARs? And how are they different?

Take a look at https://www.faa.gov/air_traffic/publications/media/AIM_Basic_dtd_10-12-17.pdf, in particular 5−2−8 and  5−4−1

The "S" means standard. So you need to know what is a departure, and what is an arrival first. Being standard helps, because everyone knows about the path and constraints associated with it. So ATC and pilot can talk about it just using the name, no need to discuss about the waypoints or altitudes that define the departure procedure or the arrival procedure.

This site has good information explaining the concept.

Both are predefined routes through the air which connect the airport areas (terminal areas) to the enroute airway system in a way remotely similar to local roads that everyone follows from and to highways. This ensures (in theory) an orderly fashion of after departure reaching (SID) and leaving towards the airport (STAR) the enroute airspaces for all aircraft.
SID stands for Standard Instrument Departure.
STAR stands for Standard Terminal Arrival Route.
The links touch upon everything else.

An additional important feature of SIDs and STARs is that they simplify ATC clearances and flight plan programming.

The "VIA" and "TO" on the PMDG 777 can accept Airways, SIDS and STARS and their transitions.
SID Stand for Standard Instrument Departure, which is a predefined route involving GPS waypoints or navigation aids. It prevents chaos near the airport airspace by having everyone exit the airspace the same way.
STAR Stands for Standard Terminal Arrival Route. This once again is a predefined route to enter the airspace Ina orderly fashion to land on a runway.


text:
How frequently are airplane windows cleaned?
When you’re driving on the highway, after sometime unwanted insects and dirt accumulate on your windshield. When you stop over at a gas station, you might clean it off. It’s likely the case for aircraft as well, especially during takeoff and landing. But how frequently are airplane windshields cleaned? And how are they cleaned? Does this include cleaning of passenger windows?

Are you interested specifically in commercial operations, or are you wondering about GA as well?

Related: https://aviation.stackexchange.com/questions/25881/do-airlines-ever-clean-their-planes

@RonBeyer commercial, but now I’m wondering about GA too

for GA airplanes you are supposed to clean the windows before every flight. This is part of the checklist. The rest of the plane is the responsibility of the owner/flight club/flight school. As long as the plane 'looks' clean, they tend to look the other way. One winter day I had to wipe off frost of the plane by hand and that definitely cleaned the plane pretty good :)

@PrashantSaraswat There is no requirement to clean GA windows before every flight, in fact you shouldn't clean them (just verify that they are clean). Excessive cleaning causes crazing/hazing. None of the checklists on the 177 I own, nor the 172 I learned in had "clean windows" as part of the preflight checklist, it may be something your school/rental company has on their checklist.

@RonBeyer I just said that it is part of my checklist. I didn't say it was legally required or was FAA mandated or anything like that. I prefer it to be on my checklist, because when I was starting I noticed that I was sitting inside with my headset on..ready to go and couldn't see a thing outside ( mostly due to frost/dew) on the windows/windscreen.

@PrashantSaraswat you said "you are supposed to clean the windows before every flight. This is part of the checklist". That's very different from saying it's something you do before every flight and is a part of your checklist, and sounds very much like you're saying it's a legal/FAA requirement or standard manufacturer recommendation.

How confusing -  I find myself agreeing with my namesake

I clean them whenever they are dirty to the point of affecting ability to see traffic or cause distractions.
Bugs, dust, and dirt can make it very difficult to spot traffic, birds, and obstructions, especially in hazy weather.
It is the pilot’s responsibility to “see and avoid” and clean windows play a large role in this critical safety area.
Depending on how bad contaminants are (i.e., if it’s bug season) the interval for cleaning could be as often as every flight or as little as once every few days while continuous flight operations are in effect.
Windows are cleaned with either water or special chemicals for cleaning plexiglass with microfiber or non-abrasive cloths. Also of note, human fingerprints are ideal for cleaning aircraft windows with water as they are soft and do not scratch, but the ridges pick up the dirt and easily rub off even sticky contaminants [bugs]. Aircraft windows are relatively soft and scratch very easily. All cleaning motions are done in the direction of the airflow to prevent hazing of the window from scratches... no circular scrubbing - only in the direction of air flow. Passenger windows rarely get dirty. It’s the ones for the cockpit that are directly exposed to the frontal airflow that get the worst of it.
I usually use water, my fingerprints for scrubbing, and clean microfiber cloths for drying to prevent water spots - which can obscure vision as bad as dirt.
Here is a video of the process.

I strongly second the water/hand method for initial cleaning of plexi.  Any windshield will have some coating of "dust" which is actually mostly silica particles along with pollen. If you just take a cloth with Mirror Glaze or some other product without a water/hand rinse first, you are literally sanding the plexi.  A great product for cleaning and polishing after the initial water cleaning is Lemon Pledge.  The lemon helps break down bugs and it doesn't streak.

I think you meant fingertips, unless you keep a baggie filled with fingerprints and sprinkle them on the window along with the water. :-)

@grumpy1arrival lol, yes I did - but it doesn’t get the point across as to why fingertips are better than a scrub brush as well as saying fingerprints does :-)

Can anyone find a video of the cleaning process?

@Pugz this copilot seems to be cleaning in a circular motion: https://youtu.be/sNGHFEaMWuI

@TayE looks like nobody ever taught him how to clean an airplane windshield :-) sadly, it exists at all levels.

@TayE I’m just being a pain. Modern jet airliner windows are made up of layers of glass, plastics, and laminates, as well as often several conductive electrical layers. This is very different from a traditional aircraft window made of just plexiglass... they must withstand the temperature of the de-icing system and also bird impacts at hundreds of knots. Either way, good practice is good practice... airflow and particles in the air always flow in the direction of airflow and it’s good not to clean against the grain.

Although this is a small subset of aviation, at the seaplane base I worked at, windows were cleaned every morning and potentially multiple times a day if salty spray got on them. It’s the pilot’s discretion, but most pilots I know prefer a clean windscreen.


text:
Can I use motor oil in a aircraft piston engine?
In one episode of the 'reality' show Airplane Repo a pilot topped off an aircraft engine with motor oil; I think it was a Cessna 182 but I may be wrong. What would be the effect on the engine? Is it a practical (and safe) alternative if aviation oil isn't available?

By motor oil, I assume that you mean automotive motor oil. In that case, it's a bad idea for a bunch of reasons. First, every airplane POH I've seen has specified that the oil must qualify to a standard - either MIL-L-6082 or MIL-L-22851 (though those have been superseded by an SAE standard). Modern automotive oil doesn't meet that standard, and therefore is effectively forbidden by the POH. More to the point, automotive oil is bad for aviation engines.
Aviation and automotive engines work on the same basic principles, but many of the details are different.1 One significant difference is that aviation engines normally burn some oil as they run, while well-performing automobile engines burn little or none.
Automotive oil contains a number of additives, such as detergents and wear inhibitors, intended for use where the oil doesn't burn off. Some of those additives do not burn completely, but instead stick around in the form of ash, where they can foul the engine and create deposits that lead to pre-ignition. That is why aviation oil is ashless dispersant: it cleans the engine by dispersing combustion byproducts into the oil (to be removed on the next oil change), while being ashless when burned. Lycoming considers it serious enough to put in an all-caps "CAUTION" section in their Lubricating Oil Recommendations document:

UNDER
  NO CIRCUMSTANCES SHOULD AUTOMOTIVE OIL BE USED. THE USE OF AUTOMOTIVE
  LUBRICANTS IN TEXTRON LYCOMING ENGINES IS NOT RECOMMENDED BECAUSE ITS
  USE COULD CAUSE ENGINE FAILURE.

If all of that wasn't enough, use of an improper oil may void your engine warranty. In short: don't use it.
References:

An editorial summary on Avweb
An aircraft engine overhauler's best practices
Lycoming's Lubricating Oil Recommendations

1) Note that I'm referring to air-cooled aviation engines that burn 100LL - made by, say, Lycoming or Continental. Rotaxes and new aero-diesels are different, and more like their respective automotive counterparts; in fact, Thielert engines are actually based on automotive diesels.

Piston engines will, in general, accept any medium-weight motor oil without complaining. While you should, also in general, use what the manufacturer specifies you can get away with quite a lot depending on the amount and your intentions. One litre low, moderate climate, short trip, planning on an oil change anyway? 7-11 brand 10W30 will be fine. Ferrying across Alaska in winter with 2 "overnight" stops? Better use the good stuff.

Automotive oil can do some serious damage to an aircraft engine: The metallic detergents can form deposits in the cylinders that lead to preignition and potentially damage the engine. This risk would logically increase in proportion to the amount of automotive oil used. It's better to carry a quart of oil with you in the plane in case you're "a little low" than to top off with unapproved oil and risk engine damage. Using (synthetic) automotive oil exclusively has other issues as well...

I agree, but that's where the "amount and future intentions" kick in. If you are 90 minutes airtime from home, are planning on changing the oil on Tuesday, and the engine is 50 hours from replacement the ash and deposits become a non-issue.

I used to read World-WarII adventure stories, one in particular rings in my mind.
A PBY landed at a remote location, in the South Pacific with one engine badly leaking oil. At the  remote base all they had had on hand was cooking oil.
The pilot ordered the engine to be filled with cooking oil, intending to get the plane off the ground, then shut it down.
But the engine was running so well, that he kept it running and running, and running, and some hours later he landed at the home base.
The crew removed the engine, then sent it to the manufacture, telling the story, at the factory,  they took the specs of the engine, and found that the cooking oil had done no damage.
The engine was fine.
.
Moral of the story, you can run cooking oil in an aircraft engine.

Welcome to Aviation.SE. Please, we are looking for factual answers, if you have a source for your statements, please edit it in. As of now your answer is sounding like a mix of hearsay and urban legend.